Modern numerical control systems for machine tools or robots may have a setting facility by which the user of such a control system is able to change the rate of motion, prespecified by a program along one or more axes, within certain limits. Thereby it is possible, for example, during the first testing of such a program, to select a clearly reduced feed speed for a tool, in order to be able to detect potential problems and still to be able to intervene at the right time. Such a setting facility, which is also referred to as an “override”, may be implemented in the form of a potentiometer, which is mounted in an easily accessible manner on the control console of the control system or on a manual control element. In that manner, one is able to affect at any time the processing speed of the respective equipment.
The setting of the potentiometer is read off in analog fashion. As the signal, for example, the voltage at the sliding contact of the potentiometer may be used. This analog signal is then conducted to an A/D converter and digitized there and made available to the control system. However, since the connection between a potentiometer and an A/D converter may, under certain circumstances, be very long, and, in addition, this connection may travel in a very rough environment, such as a machine shop floor, the analog signal is frequently encumbered with noise. As such, the digitized override signal supplied to the control system may also be noise-infested. Thus, however, that the control system may generate a noise-infested speed specification that will be comprehended by the control loop. This may lead, for example to uncleanly cut surfaces in milling and machine cutting. Therefore, it is believed to be desirable to free the digitized override signal from noise to the greatest extent possible. The use of simple filters is not believed to be effective in these circumstances, since such filters may tend to result in transient reactions and delayed responses.
In Japanese Published Patent Application No. 5-68389, for the formation of noise-filtered output values from noise-encumbered input values, it is described to accumulate the deviation between output value and input value, and to take over the input value as the new output value, and, in this context, at the same time, to reset the accumulated deviation if the accumulated deviation exceeds a certain boundary value. However, this method may have the disadvantage that the accumulated deviation, even in the case of completely random noise, after a certain time will attain any boundary value without there being any genuine change in the input value (as, for example, in the setting of the potentiometer). This effect is comparable to the Brownian motion of a molecule that is executing purely random motions, and that will still, at some time, reach every point in a space in which it is enclosed. In the case of the override signal this means that, by using such a filter, high-frequency noise components may be clearly reduced, but low-frequency components may be maintained or even additionally generated, and may have a negative effect on the work result.